The enemies in Chapter 11 are generally harder than what you've encountered before. But you should not be having trouble with fodder like the monsters in the southwestern side of Pulse (the little creatures dancing around in the circle towards a few cliffs; they aren't difficult at all and they summon monsters for more CP). You can also try fighting against Flans or monsters in Vallis Media to get used to it.
Lightning/Fang/Hope is the way to go. I generally used Hope as my party leader so I could manually handle the buffs and healing, though. If I were you, I wouldn't try my hand too much at the single Behemoths roaming the land until you hit the level cap for that area. As a rule of thumb, do not start pouring CP into your secondary roles until postgame or unless you are doing higher level mark hunts.
The general Optimas I would use with a Hope/Fang/Light party in Chapter 11 are:
Hope/Fang/Light:
Rav/Com/Rav
Rav/Sen/Rav
Rav/Sen/Com *this should be your default paradigm, imo
Med/Sen/Com
Med/Sen/Med
Syn/Sab/Med
Extras:
Rav/Com/Com (when you finally get used to fighting enemies)
Rav/Com/Rav (when you get used to fighting enemies and have beefed up a little)
Rav/Sab/Com
Rav/Sab/Rav
Hope or Vanille/Fang/Light is one of the more versatile parties before endgame, so take advantage of their skills.
If you are having trouble with Hope's overall HP, you can either give him a few HP increasing bangles, or you can swap him out for Vanille, who becomes extremely useful due to her Saboteur techniques and her Belladonna Wand/Malboro Wand. Use her Saboteur techniques to debuff and gain an advantage in battle.
Also, take note of monsters' elemental weaknesses. Use a Librascope or a weapon/accessory that gets enemies' info after you defeat them in order to see what they're weak against. This will help you out a LOT.
If you are having trouble with taking damage during battle, do not hesitate to include a Sentinel in your party. Sentinels generally Provoke enemies into attacking them (though you must be careful that a healer or something isn't standing close to them so they don't get hit with sweeping attacks or AoE attacks, but there is nothing you can do about this if they are standing close to them, which really sucks). Having a Sentinel in your party also reduces the overall damage that your party takes somewhat. So you can always go Rav/Sen/Com with a Hope/Fang/Light party.
The best place to level up on the Steppe is towards Mah'habara, where the Behemoth is fighting with another enemy. You will always get a preemptive strike. But I would not recommend doing this until you get used to fighting on the Steppe first. If you choose to do this, take the Behemoth out first because once it gets down to 1/2 its HP, it will stand up and try to recover all of its HP, rendering your PE Strike useless. This is why I say to level up before taking these two on.
I hope that helps.
